Primary vitreoretinal involvement and immunopositivity for BRAFV600E help distinguish metastatic from primary intraocular melanoma: a detailed histopathologic study of metastatic cutaneous melanoma to the eye. Histopathology 2022;80(7):1061-1070.Abstract.
OBJECTIVE: To evaluate the clinicopathologic characteristics of metastatic cutaneous melanoma to the eye and identify potential distinguishing characteristics from the more common primary uveal melanoma; particularly, tumour location within the eye, cytomorphology and immunohistochemical/specific molecular genetic features. METHODS: A retrospective observational case series using surgical enucleation and diagnostic vitrectomy cytologic specimens from seven patients with suspected intraocular melanoma, eventually diagnosed as metastatic melanoma, was conducted. Haematoxylin and eosin-stained sections of tumour and immunohistochemical (IHC) stains for BRAFV600E and Ki-67 were critically reviewed; BAP1 IHC was also evaluated in cases where additional tissue was available. Clinical imaging studies and medical records were reviewed. RESULTS: The majority of patients (86%) with metastatic melanoma have primary vitreoretinal (not uveal) involvement and epithelioid, highly malignant cytomorphology (100%); many (50%) harbour BRAFV600E mutations, a finding not seen in large cohorts of primary uveal melanoma. CONCLUSIONS: Characteristics favouring or defining metastatic intraocular melanoma over primary uveal melanoma include high-grade epithelioid cytology, predominant involvement of the vitreous cavity and/or retina, and presence of positive immunostaining for BRAFV600E.